1. Field of the Invention
The present invention relates to friction welding and, more specifically, to a tool and method for forming joints between workpieces by friction stir welding.
2. Description of Related Art
The general concept of friction stir welding is generally described in Thomas et al., U.S. Pat. No. 5,460,317; Wykes, U.S. Pat. No. 5,697,544; Colligan, U.S. Pat. No. 5,718,366; Ding et al., U.S. Pat. No. 5,893,507; Heideman et al., U.S. Pat. No. 6,053,391; Oelgoetz et al., U.S. Pat. No. 6,138,895; Rosen et al., U.S. Pat. No. 6,227,430; Colligan, U.S. Pat. No. 6,669,075; Trapp et al., U.S. Pat. No. 6,676,004; Duncan, Jr., U.S. Pat. No. 6,726,084; Carter, U.S. Pat. No. 6,758,382; Ezumi et al., U.S. Published Patent No. 2001/0004989; Andersson et al., U.S. Published Patent No. 2004/0195291; Raether et al., U.S. Published Patent No. 2005/0001009; Fuller et al., U.S. Patent No. 2005/0121497; as well as, “An Outsider Looks at Friction Stir Welding” (Federal Aviation Administration July 2005), all of which are incorporated by reference. Conventional friction stir welding is a solid state process of welding using the frictional heat generated by a non-consumable tool to join workpieces together. The friction stir welding tool includes a pin or probe that is inserted into the joint and a shoulder that is applied against an upper surface of the workpiece. The pin and shoulder rotate to generate friction needed to create a plasticized region along the joint for the welding operation.
In conventional friction stir welding operations, the weld tool often contains one or more geometrical features that promote movement of the weld material down and away from the weld tool shoulder toward the pin terminus.
The present invention relates to the surprising discovery that an improved friction weld may be made using a pin having two geometric features that move the weld material in a first direction toward the pin terminus, and in a second “counterflow” direction toward the shoulder. The first geometric feature comprises one or more tapered flats, while the second geometric feature comprises one or more channels and/or threads oriented in a “counterflow” direction.